Author Topic: Test Equipment Anonymous (TEA) group therapy thread  (Read 15698777 times)

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Offline Cerebus

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128325 on: August 02, 2022, 01:32:50 pm »
I’ll have you know it’s Lord Cthulhu who’s going to smite me.

Have you considered the advantages of converting to one of the other tentacled deities, namely Our Lord the Flying Spaghetti Monster? Instead of effete methods of cheating death, such as playing chess, that are available to other religions all the worshipers of the FSM need is a jar of tomato sauce and a fork. Should you fail in your endeavours to cheat death at least you go down with a satisfying meal inside you.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 
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Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128326 on: August 02, 2022, 01:41:26 pm »


Yes, I have... and he is arrived! The seas will soon run red with the sauce of unbelievers, and Pirates will again roam the seas, plundering your booty and serving steaming-hot pasta and marinara!

mnem
sadly, Alfredo sauce is still reserved only for the pirate-priesthood. :-[
« Last Edit: August 02, 2022, 01:42:58 pm by mnementh »
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Online TERRA Operative

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128327 on: August 02, 2022, 01:42:04 pm »
Tonight's experiment, measure rise and fall time of various 74xx14 inverter chips.

Measured at the output pin with the little spring ground terminal on the 10x probe.

Looks like the ACT and AC variants are the winners at 3.5ns, nice square wave that I was looking for.
More ringing on the ACT version though, but maybe if it were set up properly with termination resistors etc like ch_shr mentioned, it would look better?

At least I got my nice square wave now. Next step is to get it happy into 50ohms etc.
Where does all this test equipment keep coming from?!?

https://www.youtube.com/NearFarMedia/
 
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Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128328 on: August 02, 2022, 01:50:53 pm »
All this doomsday crap. I say "fuck it". Live for today. Enjoy the toys and TE now. None of us can control what happens tomorrow. When the good lord or whatever decides to collect your ticket you can't take it with you anyway.

But if the world shit does get real you just need to maintain the ability to bend over and kiss your arse goodbye.  ::)

I’ll have you know it’s Lord Cthulhu who’s going to smite me.

Lord Cthulhu does not smite... s/he/it/they consume your sanity and soul as an appetizer, then nosh on your brains before drinking various refreshments from your empty skull.

mnem
That is, if you are lucky.
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Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128329 on: August 02, 2022, 01:51:49 pm »
On the Bench Tonight: Thrift Score IR Thermometer
   Passes the reality check... it thinks my marble slab workbench is ~21°C. Everything I tried it on, it agrees within a degree against my decades-old RayTek. Unlike that, the LASER pip still work on this one.  :P   great. now I have another tool that knows more about what it's doing than I do... :-DD
Great find, I have a cheap arse one that does me, it spends most of its time sitting its box, but boy, when it comes out it to play it make swift work of finding which part on the PCB is shorting. Rather have a thermal camera, but can't afford one, but these IR sensors are pretty good. I can set a reference temp on mine and then when scanning a board, the screen will change colour from its normal green to either red or blue if the object of focus is above or below the set temp, very useful tool.   :-+

Yeah, I have a couple other ones as well... an aging RayTech that I bought off the Snap-On truck new in that brief period when I lost my mind & went back on my resolution to never work as a auto mechanic again... and a $15 Chinesium one I bought when the RayTech's LASER went tits-up. I have no idea where that one is ATM.  :-//

mnem
 :-/O
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Offline Saskia

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128330 on: August 02, 2022, 02:00:43 pm »
I’ll have you know it’s Lord Cthulhu who’s going to smite me.

Have you considered the advantages of converting to one of the other tentacled deities, namely Our Lord the Flying Spaghetti Monster? Instead of effete methods of cheating death, such as playing chess, that are available to other religions all the worshipers of the FSM need is a jar of tomato sauce and a fork. Should you fail in your endeavours to cheat death at least you go down with a satisfying meal inside you.

I'm with Odin. At least there is Meade in Valhalla.
 

Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128331 on: August 02, 2022, 02:05:13 pm »


Jeebus... is there anybody left selling on fleaBay who isn't a complete muppet...?

I just had to poke this seller with the PM stick because 10 days after I paid, it is supposed to be delivered no later than tomorrow, yet still only shows "Label Created" and not in FEDEX possession.

Do they really think nobody is gonna click on the TRACK PACKAGE button...?

mnem
fleaBay: all they actually have now is fleas.
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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128332 on: August 02, 2022, 02:05:26 pm »
Ok, so it seems the 74AC14 has an output current of 50mA per buffer. So at 4.5V supply, we get a minimum voltage of 4.4V out, which comes to 2ohms source impedance.

To impedance match this to 50ohms, If I parallel 3 buffers (max Vcc/ground current for this chip is 150mA) followed each by a 150ohm resistor, I should get 51ohms impedance, right?
« Last Edit: August 02, 2022, 02:31:18 pm by TERRA Operative »
Where does all this test equipment keep coming from?!?

https://www.youtube.com/NearFarMedia/
 

Offline BU508A

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128333 on: August 02, 2022, 02:10:23 pm »
Garibaldi's god (Babylon 5):

“Chaos is found in greatest abundance wherever order is being sought. It always defeats order, because it is better organized.”            - Terry Pratchett -
 

Offline med6753

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128334 on: August 02, 2022, 02:14:17 pm »
Since today's TE subject is centered around shelving and storage here is my contribution. The additional shelf for the TE display cabinet is finally complete and installed.



Didn't take long to fill it up. All the equipment in these two pictures has been re-capped, restored, and functional. With the obvious exception of the four duff CRT's.




And it took three dryer cycles to complete my laundry.  :rant:

Landlord has been by and believes the main clutch in the washer is shot due to assholes overloading the machine. (Not this asshole.)  :-DD
An old gray beard with an attitude.
 
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Offline ch_scr

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128335 on: August 02, 2022, 02:18:50 pm »
Ok, so it seems the 74AC14 has an output current of 50mA per buffer. So at 4.5V supply, we get a minimum voltage of 4.4V out, which comes to 2ohms source impedance.

To impedance match this to 50ohms, If I parallel 3 buffers (max Vcc/ground current for this chip is 150mA) followed each by a 15ohm resistor, I should get 51ohms impedance, right?
It's 50mA absolute max current! The 4.4V are for a current of 50uA. For a current of 24mA they give 3.86V at 25°C. (Use values closest to use case to calculate the resistance - in this case the 24mA I'd say)
In your example you would have to use 150 ohms (I think you meant to type that) in series to the (unrealistic) 2 ohm to get close to 50 ohm when parallel'd up.
« Last Edit: August 02, 2022, 02:20:37 pm by ch_scr »
 
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Online TERRA Operative

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128336 on: August 02, 2022, 02:36:29 pm »
Ok, so it seems the 74AC14 has an output current of 50mA per buffer. So at 4.5V supply, we get a minimum voltage of 4.4V out, which comes to 2ohms source impedance.

To impedance match this to 50ohms, If I parallel 3 buffers (max Vcc/ground current for this chip is 150mA) followed each by a 15ohm resistor, I should get 51ohms impedance, right?
It's 50mA absolute max current! The 4.4V are for a current of 50uA. For a current of 24mA they give 3.86V at 25°C. (Use values closest to use case to calculate the resistance - in this case the 24mA I'd say)
In your example you would have to use 150 ohms (I think you meant to type that) in series to the (unrealistic) 2 ohm to get close to 50 ohm when parallel'd up.

Ah ok. So If my supply is 5.0V, then I could assume I get a volt drop of say 1.14V then?
So with a current of 24mA then I'd have a source impedance of 47.5ohms, which would call for roughly 100ohm resistors?
Where does all this test equipment keep coming from?!?

https://www.youtube.com/NearFarMedia/
 

Online themadhippy

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128337 on: August 02, 2022, 02:38:08 pm »
speed cameras are not a revenue raising device,thats why theres often a mobile one parked immediately after the 30 sign near here, said sign is just after a bend so you dont see it until its almost too late.Heres a crazy idea,why not put countdown markers ,like you have on motorways,leading upto the speed reduction,surely that would be much safer than suddenly having to slam the anchors on.
 

Offline med6753

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128338 on: August 02, 2022, 02:38:39 pm »
An old gray beard with an attitude.
 

Offline tggzzz

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128339 on: August 02, 2022, 02:43:21 pm »
Ok, so it seems the 74AC14 has an output current of 50mA per buffer. So at 4.5V supply, we get a minimum voltage of 4.4V out, which comes to 2ohms source impedance.

To impedance match this to 50ohms, If I parallel 3 buffers (max Vcc/ground current for this chip is 150mA) followed each by a 150ohm resistor, I should get 51ohms impedance, right?

See https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg1902941/#msg1902941

You will need to pay careful attention to PSU decoupling, including lead length inside the package (hint: pins 14+7 is just about the worst choice that could have been made)
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 
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Offline ch_scr

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128340 on: August 02, 2022, 02:44:27 pm »
Ok, so it seems the 74AC14 has an output current of 50mA per buffer. So at 4.5V supply, we get a minimum voltage of 4.4V out, which comes to 2ohms source impedance.

To impedance match this to 50ohms, If I parallel 3 buffers (max Vcc/ground current for this chip is 150mA) followed each by a 15ohm resistor, I should get 51ohms impedance, right?
It's 50mA absolute max current! The 4.4V are for a current of 50uA. For a current of 24mA they give 3.86V at 25°C. (Use values closest to use case to calculate the resistance - in this case the 24mA I'd say)
In your example you would have to use 150 ohms (I think you meant to type that) in series to the (unrealistic) 2 ohm to get close to 50 ohm when parallel'd up.

Ah ok. So If my supply is 5.0V, then I could assume I get a volt drop of say 1.14V then?
So with a current of 24mA then I'd have a source impedance of 47.5ohms, which would call for roughly 100ohm resistors?
Well at 4.5V the drop is 0.64V which gives ~27ohms. At 5.5V the drop is 0.64V as well which gives the same 27ohm. Often you see lower output impedances at higher voltages though!
I'll take the average of the 4.5V and 5.5V impedance values to get close to a "at 5V" value. But that's probably gilding the lily and the 4.5V value is more than good enough...
So I'd say take 120ohms in series each, parallel these bad boys up and don't forget to load them with 50R [at the scope (check for maximum power of the internal termination though and use an external one if need be!)]
 

Offline dl6lr

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128341 on: August 02, 2022, 02:44:31 pm »
Just watched that a parcel has been delivered to my home. There should be new old Tek equipment in it, so I will unbox it this evening and post some pictures, stay tuned.
Not the one from med, it has passed customs and is on the way to me. So I suspect I have to collect it from the post office, as they are not able to collect money for customs any more  :palm:

Just signed a contract to install solar cells on my roof. Lead time for the solar inverter is several months... Lead time for the battery is nearly a year...
 
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Offline med6753

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128342 on: August 02, 2022, 02:46:40 pm »
Just watched that a parcel has been delivered to my home. There should be new old Tek equipment in it, so I will unbox it this evening and post some pictures, stay tuned.
Not the one from med, it has passed customs and is on the way to me. So I suspect I have to collect it from the post office, as they are not able to collect money for customs any more  :palm:

Just signed a contract to install solar cells on my roof. Lead time for the solar inverter is several months... Lead time for the battery is nearly a year...

I hope they don't rip you off on custom's charges.  :o
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Offline bd139

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128343 on: August 02, 2022, 02:52:14 pm »
I’ll have you know it’s Lord Cthulhu who’s going to smite me.

Have you considered the advantages of converting to one of the other tentacled deities, namely Our Lord the Flying Spaghetti Monster? Instead of effete methods of cheating death, such as playing chess, that are available to other religions all the worshipers of the FSM need is a jar of tomato sauce and a fork. Should you fail in your endeavours to cheat death at least you go down with a satisfying meal inside you.

Already sold my soul to the church of the subgenius  :popcorn:
 
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Offline dl6lr

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128344 on: August 02, 2022, 02:54:11 pm »
I hope they don't rip you off on custom's charges.  :o

Usually you have to pay 19% VAT plus a fee for DHL.
 

Online TERRA Operative

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128345 on: August 02, 2022, 03:01:25 pm »
Ok, so it seems the 74AC14 has an output current of 50mA per buffer. So at 4.5V supply, we get a minimum voltage of 4.4V out, which comes to 2ohms source impedance.

To impedance match this to 50ohms, If I parallel 3 buffers (max Vcc/ground current for this chip is 150mA) followed each by a 15ohm resistor, I should get 51ohms impedance, right?
It's 50mA absolute max current! The 4.4V are for a current of 50uA. For a current of 24mA they give 3.86V at 25°C. (Use values closest to use case to calculate the resistance - in this case the 24mA I'd say)
In your example you would have to use 150 ohms (I think you meant to type that) in series to the (unrealistic) 2 ohm to get close to 50 ohm when parallel'd up.

Ah ok. So If my supply is 5.0V, then I could assume I get a volt drop of say 1.14V then?
So with a current of 24mA then I'd have a source impedance of 47.5ohms, which would call for roughly 100ohm resistors?
Well at 4.5V the drop is 0.64V which gives ~27ohms. At 5.5V the drop is 0.64V as well which gives the same 27ohm. Often you see lower output impedances at higher voltages though!
I'll take the average of the 4.5V and 5.5V impedance values to get close to a "at 5V" value. But that's probably gilding the lily and the 4.5V value is more than good enough...
So I'd say take 120ohms in series each, parallel these bad boys up and don't forget to load them with 50R [at the scope (check for maximum power of the internal termination though and use an external one if need be!)]

Here we are with the three buffers followed each by their own 120ohm resistor then all connected to a BNC, then to the scope with a HP passthrough 50ohm terminator.

Not sure that the P-P voltage is enough to be reliably used for TTL stuff?
Where does all this test equipment keep coming from?!?

https://www.youtube.com/NearFarMedia/
 

Offline med6753

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128346 on: August 02, 2022, 03:03:50 pm »
I hope they don't rip you off on custom's charges.  :o

Usually you have to pay 19% VAT plus a fee for DHL.

Yikes. That sucks. Fucking bandits.  :o
An old gray beard with an attitude.
 
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Offline med6753

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128347 on: August 02, 2022, 03:10:45 pm »
Started tear down of the B&K 2120. Top board removed. All modular, no unsoldering required.



Those 2 shields must be removed to gain access to the channel attenuator switch decks for cleaning. They are soldered to the board.



The replacement capacitors will be delivered tomorrow.
An old gray beard with an attitude.
 
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Offline Brumby

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128348 on: August 02, 2022, 03:11:45 pm »
Oh no, I went and built more shelving for the TE that's currently piled in the corner, but it's twice as big as it needs to be and now the void keeps telling me to browse ebay!!  :scared:

McBryce.

LOL. I just did something similar. Bought three large plastic crates to move TE stuff in and worked out they are now not even half full. Need padding. Quick!!!

There we go!   :-+
 
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Offline Cerebus

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #128349 on: August 02, 2022, 03:27:57 pm »
When scanning, how frequenty should you take your eyes off the road for a couple of seconds? That's to re-focus on the digital display, read the numbers (ugh, but that's the modern way), re-focus on the road.

A lot can happen in a couple of seconds.


The solution to that problem, if it is a real problem, is a heads up display that reproduces essential dashboard information where it's easy to see. In fact many modern cars have this, either as standard or as an extra cost option. There are third party heads up display solutions available. Some dedicated, some that include mounting a phone so that it reflects a speed indication off the windscreen.

In practice glancing at the speedometer doesn't take 2 seconds, more like 200 - 300 ms and you only need to do so if you've substantially changed your speed upward, so much so that you can't internally estimate whether you're still within the speed limit. One glance at one's speedometer every 30 seconds will consume 1% of one's attention, the other 99% can stay on the road.

As it is, my own experience is that I can largely ignore the speedometer and set my speed by the conditions and later review of dashcam recordings complete with GPS derived speed show that that I'm automatically keeping below the speed limit (without any real audio cues; my current hybrid car is very, very quiet to the point that I often only notice that it's switched the petrol engine on by the position of the rev counter needle). On most urban roads my speed is often much further below the speed limit than one would think; limited mostly by the hazards that are in view, I rarely travel over 25 mph.

In the UK knowing what the current speed limit is, is trivial. You're either on a lit urban road where the limit is 30, a national speed limit road outside town where  the existence of a central reservation tells you whether the limit is 60 mph or 70 mph. For everywhere else there will be clear speed limit signs by the side of the road where limits change, with repeater signs every 200m or less for 20 mph limits, scaling up to repeater signs every 600m or less on 70 mph roads. The first repeater sign after a limit change will be at most 200m for a 20 mph limit and 450m for a 70 mph limit.

Thus if you're in any doubt what the current limit is on a posted road you have an average of between 100m (11s) and 300m (9.6s) until you pass the next repeater, therefore absolute maxima of 22 and 19 seconds for 20 mph and 70 mph respectively. Most likely one will be able to see and read it sooner.

With all that in mind I don't think there is any excuse for not knowing the current speed limit, and to my mind any justification that one needs a speed camera warning system to avoid inadvertently exceeding the speed limit thus fails. All that is required to avoid prosecution is to (1) pay sufficient attention to what the limits are, (2) sufficient attention to what one's speed is, and (3) sufficient attention to bright yellow boxes stuck on posts at the side of the road with the warning signs that precede them. If one is already paying sufficient attention to the many hazards on the roads, taking in those three bits of information is trivial compared to the unpredictability of other road users.

Speed cameras don't catch speeders, they catch inattentive drivers and I'm all for that. It's not speed that kills, it's inattention.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 
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